Firewall connectors started off as simple 8-10 wire plugs located on each side of the firewall and allowed the engine to be pre-wired before it hit the line. Mistakes in this light we dramatically reduced. In the 1960s when accessories started drawing more juice, the firewall plug started to show more of its shortcomings. When ever you �€�un�€�wire a car for restoration, look at the wires and determine where the damage is. There will be some in the middle of a length of wire where some previous owner might have spliced something in. There will be some damage in the engine compartment where repair activity might have smashed a wire or damaged the insulation. Where is the worst? The burns, the melting? At the factory connectors and fire wall plugs

These firewall connectors have terminals made of brass and are pressed together with friction and held there by a plastic housing which is busy trying to hold up to 20 or 30 other wires in place. The result is three sources or trouble. One being the wire to the terminal, second the two terminals and third the other terminal to the last wire. The result is a clear source of trouble and proven by the melted housing. WIRE WORKS has learned from these indicators and manufacturers their harnesses with out the need for a connector. In a vehicle being wired one off the straight copper wire can produce up to 80 percent more current without the risk of failure.

Brass can only carry 12-16% of the amperage the a similar sized copper terminal can carry. Copper of course is too soft for use in smaller applications. Between the loss of capacity and the other crimps and connections, certainly a straight piece of copper wire (times the number of circuits in the plug) can work for you much better

We have to use connectors in some locations between switches and wires or other sensors and wires but why use them where we don�€™t have to? I started my career wiring cars with the 1960s Mopar vehicles that had firewall plugs that failed in use. I spent a lot of time splicing around the firewall connections to reconnect circuits. Reproduction harness have the wonderful points but I suggest to you that unless you are trying to �€�reproduce a factory vehicle, the connectors in the firewall need to be considered. IF you want to make a more reliable system eliminate that plug.
Look at what made the original fail, look at age and technology of the fire wall plug AND the fuse box. Did the fusebox have some melted areas? Why put back the same technology that failed under less load than you intend to put it thru. Are you planning A/C? Power windows? Do you think the original fuses held up OK without these heavy options? Plan ahead and consider modern technology.